In recent years, motors are increasingly demanded to be used for drive power of vehicles. Such motors used for drive power of vehicles are requested to reduce size and increase power. As one method for such a purpose, a method using a flat conductor for a coil has been studied. This is because the use of the flat conductor for a coil allows an increase in cross sectional area and improvement in lamination factor. In the case of a motor using a coil, it is necessary to insert the coil in slots of a stator. However, in many cases, slots have a trapezoidal shape. From the geometrical viewpoint, a rectangular cross section enables a lower void ratio than a circular cross section. This tendency more remarkably appears as the cross sectional area is larger. Accordingly, a flat conductor having a rectangular cross section can provide a wider cross sectional area, which is likely to increase the lamination factor.
Patent Document 1 discloses a technique related to a rotary electric machine for a vehicle. In a stator core formed of stacked electromagnetic steel plates, four corners of each slot are made in circular arc shape and a coil inserted in each slot is formed in rounded or curved shape in correspondence with the circular arc shape of each slot. Of the coils inserted in the slots, accordingly, flat conductor parts on an outermost circumference and an innermost circumference are deformed correspondingly. This results in an increase in lamination factor of a stator and an increased contact area between the stator core and each coil. Thus, an efficiency of heat transfer can be enhanced.
Patent Document 2 discloses a technique related to a method for producing a coil. A coil wire is wound around a bobbin, and then the bobbin is expanded to widen the inner diameter of the coil and external force is imparted from outside to the coil by use of a die or the like, so that a flat conductor forming the coil is plastically deformed to bring the wires into close contact with each other. Thereafter, the coil is subjected to an insulation treatment and inserted in the stator core. This can increase the lamination factor.
Patent Document 3 discloses a technique related to a method for producing an armature. A core of the armature is constituted so that a plurality of coils are arranged circumferentially. On opposite side surfaces on a coil side, an electric wire is wound to form a coil around a teeth part having surfaces almost parallel to a coil side boundary surface and steps nearly equal to the integral multiple of the average thickness of the layers or turns of the coil. As a result, the coil is placed in close contact with the core and mutual contact degree of the conductors is also increased. The lamination factor can therefore be enhanced.
Patent Document 4 discloses a technique related to assembled conductors. An adhesive layer is provided on an outer periphery of an insulation coating layer that insulates flat conductors. This can enhance the mutual contact degree of the flat conductor, resulting in an increase in lamination factor.
Patent Document 5 discloses a technique related to a rotary electric machine for a vehicle. Two flat conductors are insulated together in pairs, so that an insulation layer between the paired flat conductors can be made thin. Further, the outer periphery of the paired two flat conductors is formed in a curved shape. Inner four corners of each slot are formed in circular arc shape and the shape of the flat conductor is correspondingly designed. This can contribute to an increase in lamination factor.
Patent Document 6 discloses a technique related to a stator and a method for producing the same. Of conductors placed in a stator core, a conductor disposed on a near side to a teeth part is designed to have a circular cross section. This conductor is wound around the stator core and applied with pressure from outside after a first layer is formed. Thus, the contact degree of conductor parts is enhanced. Thereafter, another conductor having a rectangular cross section is wound as a second layer on a side far from the teeth part, thereby providing a double-layer structure. This can reduce a dead space and contribute to an increase in lamination factor of a stator.